1. Field of the Invention
The present invention relates to a white light emitting device, more particularly to a monolithic white light emitting device in which a plurality of active layers are configured into a single device to generate light of at least two different wavelengths, and a manufacturing method thereof.
2. Description of the Related Art
In general, an LED-based white light emitting device is widely utilized as lightening devices or backlights of display devices. In broadly known methods to obtain such a white light emitting device, blue, red and green LEDs manufactured separately are simply combined or a fluorescent substance is employed. But combining multi-colored separate LEDs on a printing circuit board requires a complicated driving circuit therefor, disadvantageously rendering it hardly miniaturizable. Therefore, recently, a method for manufacturing the white light emitting device via the fluorescent substance has been commonly used.
In conventional manufacturing methods using the fluorescent substance, a blue light emitting device or an ultraviolet ray light emitting device is employed. For example, in case of use of the blue light emitting device, blue light is wavelength-converted into white light via a YAG fluorescent substance. That is, blue wavelength generated from the blue LED excites the Yittrium Aluminum Garnet (YAG) fluorescent substance to finally emit white light.
FIG. 1 is a cross-sectional view illustrating an overall structure of a conventional white light emitting device 10 using a YAG fluorescent substance. FIG. 1a depicts an InGaN-based blue LED 9 mounted on a cap of a lead frame 2 and the YAG fluorescent substance 5 enveloping the blue LED 9 inside the cap. Also, the blue LED 9 is wired to a cap-structured anode lead frame 2 and a cathode lead flame 4. An upper part of all the lead frames 2 and 4 having the blue LED 10 positioned therein is molded with a transparent material 7.
If current is applied through the lead frames 2 and 4 and blue light is generated from the InGaN-based blue LED 9, some portions of the blue light excite the YAG fluorescent substance 5. At this time, the YAG fluorescent substance is characteristically excited at 460 nm, i.e., a peak wavelength of the InGaN blue LED 10, thereby emitting yellow-green fluorescent light. The yellow-green fluorescent light obtained via the YAG fluorescent substance 5 synthesizes with some other portions of the blue light directly emanated from the blue LED 9 to finally emit the white light.
The white light emitting device shown in FIG. 1 advantageously does not require current control necessary for combining respective RGB LEDs. However, the conventional light emitting device has limitations in that fluorescent powder adversely affects properties of the device, or excellent color feeling is hardly attainable due to decreased light efficiency and color correction index in exciting the fluorescent substance.